Method and apparatus for controling synchronous machines



July 9, ma H, T. @EMV METHOD AND APPARATUS FOR CONTROLLING SYNCHRONOUS MACHINES Fil'ed Aug. 18, 1938 XTM/QTTCQP: Harold. T Seeey Patented July 9, 1940 UNITED STATES METHOD AND APPARATUS FOR CONTROL- LING SYNCHRNOUS lMACHINESl Harold T. Seeley, Lansdowne, Pa., assigner/to General Electric Company, a. corporation of New York Application August 1s, 193s, serial No. 225,609

4 Claims.

My invention relates toa method and apparatus for controlling synchronous machines and particularly to a method and an arrangement of apparatus for varying the primary connections 5 of a synchronous machine. One object of my invention is to provide an improved method and an improved arrangement oi apparatus for eecting the transfer from the reduced voltage starting to the full voltage running primary connections of a synchronous machine without producing any substantial disturbances in the electrical condi tion of the supply circuit.

My invention will be better understood fromv the following description when taken in connection with the accompanying drawing, Fig. l oi which diagrammatically illustrates a synchronous motor starting system embodying my invention and Fig. 2 of which is an explanatory vector diagram of the starting voltages applied to the motor primary winding in the particular embodiment oi my invention shown in Fig. l, and its scope will-be pointed out. in the appended' claims.

Referring to Fig. 1 oi the drawing, i represents a synchronous machine, such as a synchronous condenser or motor having a polyphase primary or amature winding 2 and a field winding 3. The primary winding 2, which is shown as a three-phase winding, has its three terminals 2a 2b and 2c arranged to be connected directly to the conductors la, 4b and 4c, respectively, of a three-phase supply circuit 4 by suitable switching means 5. B represents a suitable switch for connecting the motor terminals 2a, 2h and 2c to the low voltage terminals of suitable voltage reducing means such as an auto-transformer i the windings of which are connected to the supply circuit 4 and to each other in any suitable inanner so that the low secondary voltage thereof leadsthe voltage of the supply circuit 4 by a predetermined amount. 8 represents a two-position eld switch which in one position connects, through its contacts i2, a discharge resistor d across the terminals of the field, winding t and which in its other position connects, through its contacts Il, a source of excitation i and a sultable adjustable resistor ii in series across the terminals ofv the ieid Winding 3.

In accordance with my invention, overexcite 50 the eld winding 3 while the starting switch 6 is closed and, also, I interconnect the windings of the auto-transformer. l in any suitable manner so that the low polyphase starting voltage impressed across the motor terminals 2a, 2b and 5 2c is advanced in phase a. predetermined amount relative to the phase voltages between the conductors lla, 4b and lo of the supply circuit 4. Preferably the amount of overexcitation is so ad- .iusted that, when the switch 8 is opened after w the motor has been synchronized, the terminal (Cl. 17h-118) voltage of 'the motor' will build upquickly to its normal running value and the low polyphase starting voltage is advanced in phase angle by an amount equal to the angle by which the motor will fall back during the transfer from low voltage to full voltage primary connections when the transfer is prolonged just long enough to allow the motor terminal 'voltage to increase to its normal running value. In this manner the switch 5 is closed at an instant when the motor terminal voltage is substantially in phase and equal in magnitude with the supply circuit voltage so that no sudden rush of current occurs to produce undesirable disturbances in the supply circuit d. For automatically effecting the closing of the switch E at the proper time after the switch 6 is opened, I have shown a time relay i9 the energizing circuit oi which is completed through the series connected contacts 2li of the iield switch t and contactsZi of the switch 65. The relay it is adjusted so that its operating time is long enough so that it closes its contacts 22 in an energizing circuit for the closing coil 23 of the switch c to eect the closing of the switch t when motor terminal voltage is in phase and' equal in magnitude with the voltage of the supply winding is arranged to be connected to the motor terminal 2a by the switch 6 and one end of the winding 1c is connected to the conductor 4c of the supply circuit 4 and the other end of the winding 1c is arranged to be connected to the motor terminal 2b by the switch 8. The three windings 1a, 'ib and 'lc are also interconnected at dissimilar points so that the corresponding re spective intermediate portions XZ, YX and ZY- are connected in delta. The voltages obtained by Similarly, one end of the the connections of the windings la, 1b and. lc,

shown in Fig. 1, will be seen more clearly from the vector diagram, shown in Fig. 2. In this Fig. 2, 4a, 4b and 4c represent the delta voltage between the conductors 4a, 4b and 4c. XYZ represents the delta voltage across the intermediate delta-connected portions of the windings 1a, 1b and 1c and the delta voltages 2a, 2b and 2c represent the voltages applied to the motor terminals 2a, 2b and 2c. From this Fig. 2, it will be seen that the phase of each secondary voltage of the auto-transformer 'l leads the corresponding phase voltage of the supply circuit 4 by a predeterrelatively low leading voltage impressedl across the armature winding 2 by the autotransformer 'l causes the machine l to start from rest and accelerate to substantially synchronous speed as an induction motor. When the motor l reaches a speed near synchronous speed, the field switch 3 is operated in any suitable manner so that the source of excitation l@ and the adjustable rheostat ll are connected in series with the eld winding il to pull the motor l into'synchronism. The rheostat il is adjusted so that the machine Als overexcited a predetermined amount. Since the vvoltage impressed across the armature winding of the motor l leads the voltage of the supply circuit Ll, the rotor of the motor l, while it is operating in synchronisrn with the impressed low voltage, is also ahead of the position it would occupy ii the motor were operating in synchro nisrn, with its armature winding connected di rectly to the supply circuit il by the running switch 5.

'When it is desired to establish the normal running primary connections ci the 'motor after the motor has been synchronized, the switch is iirst opened to disconnect the armature winding 2 from the secondary terminals oi the auto trans= former l. By closing its contacts Mythe switch li completes ,an energizing circuit for the time relay l@ through contacts il@ of eld switch il. Due to the fact that the machine is overeucited, the terminal voltage ci the machine starts to increase as soon as the switch is opened and after a predetermined time the terminal voltage oi the machine reaches a value equal to the supply circuit voltage al. also. as soon as the switch t is open, the rotor or the machine i starts to slotvrup so that the motor terminal volt age starts to fall loaclr relative to the supply circuit voltage.

those skilled in the art, and I therefore aim in the appended claims to cover all such changes and modifications as tall within the true spirit and scope oi' my invention.

What l claim as new and desire to secure hy Letjrs Patent of the United States is:

l lbflhe methodloi varying the voltage applied to the armature'f'windinu of a synchronous ruaniter a predetermined time, equal to the stun of the delay oi relay and the diagrammatically indicated,

e which is operating in synchronism with a relatively low voltage source of alternatingctirrent, which consists in disconnecting the armature winding of the machine from said source while maintaining its eld winding excited with direct current of such a magnitude as to cause the terminal voltage of the disconnected machine to build up to a predetermined relatively high voltage within a predetermined time interval, and then connecting at the expiration of said predetermined time interval the armature winding of said machine to 'a source oi alternating e current having a voltage substantially equal to said relatively high voltage and lagging the voltage o said relatively low voltage source anv amount substantially equal tothe phase variation of the armature terminal voltage ot the disconnected machine occurring during said predetermined tirne interval.

2. in combination, a polyphase supply circuit, a synchronous machine, means including a transformer interconnecting said supply circuit and machine lor applying to said roachme a relatively low polyphase voltage advanced in phase relative to the voltage o said supply cir cult, means roroverezrciting said machine while.

said low voltage'. is applied thereto, switching means for disconnecting said machine from said transformer, and means for connecting said mace directly to saidcircuit after said machine has beenl disconnected irorn said transformer for a sudcient length ci time to allow the terminal voltage oi said machine to build up to a value substantially equal in magnitude to the supply voltage ci said machine to iall haci?. in phase suillciently to be in phase with the supply circuit voltage and to build up to a valve substantially equal in' magnitude to the supply circuit voltage.

e. The method of changing the voltage applied to a synchronous machine, which consists in operating the machine in synchronism with a relatively low voltage source oi alternating current which leads the voltage ci a relatively high voltagesource or" alternating current by a predetermined aniount, then entirely disconnecting bring' the voltage oi said machine substantially into phase with the voltage of said relatively voltage source, and then connecting said :nice to said relatively high voltage source when the voltages thereof are substantially equal and in phase. 

